The long-range goal of this program are to learn how vertebrate olfactory receptor neurons detect and discriminate different odors. The study will use the mudpuppy, Necturus maculosus, an aquatic salamander with large cells that are well suited to patch-recording techniques. Receptor neurons will be isolated without enzymes to preserve their chemo-sensitivity, and studied using odorants which we have shown to stimulate the mudpuppy olfactory system in vivo. We have also shown that Xenopus oocytes injected with mRNA prepared from olfactory tissue can become sensitive to odor molecules. We will use this expression system and molecular biological techniques to identify and characterize receptors and other elements of olfactory transduction pathways. There are four specific aims for the next program period. 1. Characterize the cellular mechanisms used for detection of amino acids and aromatic compounds in dissociated olfactory neurons. 2. Examine the basis of chemo-sensory discrimination by evaluating the sensitivity exhibited by individual olfactory neurons. 3. Determine the origin of the receptor potential, identifying the ionic conductances which underlie it and how they are modulated by chemical stimulation. 4. Identify and characterize receptors and other components of the olfactory transduction pathways by expression in oocytes of mRNA from the olfactory epithelium. The suitability of the preparations and the feasibility of the methods have been demonstrated, providing strong assurance that the study will yield useful results.